Dual Transfer Mode (DTM) is specified in 3GPP TS 43.055 V6.7.0 (2004-11), 3rdGeneration Partnership Project; Technical Specification Group GSM/EDGE, Radio Access Network; Dual Transfer Mode (DTM); Stage 2 (Release 6).
Although Dual Transfer Mode (DTM) Enhancements have been standardized for GERAN A/Gb mode in 3GPP Release 6 there is a need to define improvements enabling DTM (PS+CS) handover in order to minimize the PS end-to-end delays in DTM when a delay-sensitive PS data flow is on-going. The details of a handover of CS resources is being standardized for general handover purposes in 3GPP TS 23.009 V6.0.0 (2004-12), Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Core Network; Handover procedures(Release 6). The handover of PS resources is being standardized for general purposes in the 3GPP TSG (Technical Specification Group) “GERAN” (GSM (Global System for Mobile Communication) EDGE (Enhanced Data Rates for GSM Evolution) Radio Access Network) in the technical specification 3GPP TS 43.129 v6.0.0 (2004-11), 3rd Generation Partnership Project; Group GERAN, Packet-switched handover for GERAN A/Gb mode; Stage 2 (Release 6).
The maximum service interruption tolerable by real-time PS services is 150 ms. The interruption of the PS service introduced at handover (of the CS service) in DTM is 3.4 s in the Inter-BSC—Inter-MSC—Inter-SGSN DTM case with approximately 2.7 s induced by Routing Area Update G2-040049. An enhancement to improve the PS handover situation is shown in co-owned, co-pending U.S. provisional application Ser. No. 60/672,686 entitled “Enhancement of a Circuit-Switched (CS) handover procedure to support handover of Packet-Switched (PS) services, including a method to synchronize the handover of PS and CS resources” filed on even date herewith and which is hereby incorporated by reference for background. The invention described in the co-pending application improves PS handover and is to be proposed by the assignee hereof for adoption in TSG GERAN TS 43.129 to provide a solution to the service interruption problem for PS services upon cell change. In the disclosure thereof, the existing principles of CS and PS handover are utilized to enhance the performance of DTM in terms of end-to-end delay.
As shown in FIG. 1 hereof, TS 43.129 shows a reference architecture for PS handover in GERAN A/Gb mode including a Core Network (CN) with an MSC connected to a first SGSN via a Gs interface, the first SGSN connected to a second SGSN and to a GGSN via Gn interfaces, the MSC also connected to a PSTN with the first SGSN connected to other networks via a Gp interface, and with the GGSN connected to other networks via Go and Gi interfaces. For the radio access network, a BSS/GERAN is shown connected to the MSC of the CN via an A interface and to the first SGSN via a Gb interface. The BSS/GERAN includes a BSC connected to BTSs by Abis interfaces. One of the BTSs is shown in communication with an MS via a Um (wireless) interface. An RNS (or another BSS) is also shown with an RNC (or BSC) connected to NodeBs each having cells with Uu interfaces also capable of communicating with the MS. The NodeB is a logical node responsible for radio transmission/reception in one or more cells to/from the User Equipment. It terminates the Iub interface towards the RNC. The RNC (or BSS) is shown connected to the MSC via an IuCS interface and to the second SGSN via an IuPS interface. The figure shows both user traffic and signalling on most of these interfaces. Besides the problem solved by the above-mentioned, co-owned U.S. provisional application, there is still another problem. As presently specified, during the handover of the CS resources, the BSS initiating the handover (the “source” BSS) sends to the MSC a list of BSSs (Cell Identifier list (preferred) Information Element (IE)) from which the MSC will choose one BSS as a target BSS for handover of the CS resources. During the handover of the PS resources the BSS initiating the handover selects one Target Cell based on the received measurement reporting and sends this further to the SGSN. In the DTM handover case, the SGSN does not have any knowledge about the target BSS chosen by the MSC from the list and in some cases there may not be any direct connection between the MSC and the SGSN.